Disconnector

ABSTRACT

A disconnector for a surge arrester explosively separates an electrical lead, normally a ground lead, from the arrester to prevent a permanent fault on a circuit and to provide an indication of a failed arrester. The disconnector includes means for the direct or positive venting of the interior of the housing of the arrester to the disconnector prior to the operation of the disconnector and to the atmosphere subsequent to the explosive operation of the disconnector. The disconnector further includes means for creating a relatively large air gap to aid in extinguishing an electrical arc thereacross and in interrupting the flow of continuous follow current upon the explosive operation of the disconnector. Finally, one embodiment of the inventive disconnector includes an insulating housing having a reduced thickness portion to increase the capacity or ability of the disconnector housing to fracture in response to the application of tensile forces as a result of the explosive operation of the disconnector. This embodiment of the disconnector further includes bridging or strengthening material disposed over at least a portion of the reduced thickness portion of the disconnector housing to increase the capacity or ability of the disconnector housing to withstand the inadvertent application of compressive forces without fracturing.

United States Patent [191 Cunningham et al.

[ DISCONNECTOR [75] Inventors: Francis V. Cunningham, Western Springs; John S. Wiclks, Glen Ellyn, both of 111.

[73] Assignee: Joslyn Mfg. and Supply Co.,

Chicago, Ill.

22 Filed: May 30, 1973 [211 App]. No.: 365,164

[52] US. Cl 317/61, 317/66, 317/71 [51] Int. Cl. H02h 3/22 [58] Field of Search 317/61, 62, 66, 70, 71,

[ 56] References Cited UNITED STATES PATENTS 2,548,112 4/1951 Kaminky 317/66 3.291937 12/1966 Carothers et a1. 337/30 3.679938 7/1972 Carothers et a1. 317/66 X 3,702,419 11/1972 Carothers et a1. 317/66 X 3,710.212 l/l973 Marek et a1. 317/66 Primary E.\'amitter.l. D. Miller Assistant Ermniner-Patrick R. Salce Attorney, Agent, 0" Firm-Mason, Kolehmainen, Rathburn & Wyss [111 3,869,650 1 1 Mar. 4, 1975 [57] ABSTRACT A disconnector for a surge arrester explosively separates an electrical 'lead, normally a ground lead, from the arrester to prevent a permanent fault on a circuit and to provide an indication of a failed arrester. The disconnector includes means for the direct or positive venting of the interior of the housing of the arrester to the disconnector prior to the operation of the disconnector and to the atmosphere subsequent to the explosive operation of the disconnector. The disconnector further includes means for creating a relatively large air gap to aid in extinguishing an electrical arc thereacross and in interrupting the flow of continuous follow'current upon the explosive operation of the disconnector. Finally, one embodiment of the inventive disconnector includes an insulating housing having a reduced thickness portion to increase the capacity or ability of the disconnector housing to fracture in response to the application of tensile forces as a result of the explosive operation of the disconnector. This embodiment of the disconnector further includes bridging or strengthening material disposed over at least a portion of the reduced thickness portion ofthe disconnector housing to increase the capacity or ability of the disconnector housing to withstand the inadvertent application of compressive forces without fracturing.

43 Claims, 8 Drawing Figures 1 IDISCONNEC'IOR BACKGROUND OF THE INVENTION A. Field of the Invention 1 The device of the present invention generally relates to an apparatus for protecting electrical equipment from damage or destruction due to the presence of electrical overvoltage surges, commonly referred to as a surge or lightning arrester and, more particularly, to a valve-type arrester, and, more specifically, to a new and improved device for separating an electrical lead therefrom, commonly referred to as an electrical disconnector.

B. Description of the Prior Art A surge or lightning arrester is commonly electrically connected across a comparatively expensive piece of electrical equipment to shunt overvoltage surges, for example, overvoltage surges due to lightning strokes, to ground to thereby protect the piece of electrical equipment from damage or destruction due to'the overvoltage surges. Occasionally, the arrester itself is damaged by a relatively large overvoltage surge. The damaged arrester may then continuously conduct follow current or fault current subsequent to the overvoltage surge and thus cause a circuit fuse to blow or a circuit breaker to trip.

Many distribution class valve-type arresters are provided with explosive electrical disconnectors for disconnecting electrical leads from the arresters after the arresters fail to operate properly as a result of damage thereto. The following United States patents disclose several typical prior art ground lead disconnectors: U.S. Pat. Nos. 2,860,210; 3,100,246; 3,369,091; 3,679,938; 3,702,419; and 3,710,212. Each of these prior art disconnectors contains an explosive cartridge that, when sufficiently heated, ignites a charge of explosive material to separate an electrical lead connected to one longitudinal extremity of the arrester from the arrester.

These disconnectors are designed to be explosively inoperative when the arresters discharge the overvoltage surges and interrupt the follow currents in the normal manner. However, when the arrester fails to interrupt the follow current after an overvoltage surge, as in the case of damage to the arrester, the disconnector is designed to ignite the explosive cartridge to separate an electrical lead from the arrester and to thereby remove the arrester from the circuit to enable subsequent circuit operation. The separation of the electrical lead, typically a ground lead, from the arrester further provides a readily apparent visual indication to a workman that a particular arrester has failed and must be replaced.

While these typical prior art disconnectors function adequately to disconnect electrical leads, they are typically ineffective in preventing the fracture and explosion of an associated arrester housing as a result of the continuous flow of follow current through the arrester. The interior of the housing of an arrester is typically hermetically sealed to prevent moisture from entering and damaging the internal components of the arrester. The flow of follow current through the arrester and especially through the one or more valve blocks of a valve-type arrester, volitalizes the resistive material of the valve blocks and thereby causes the presence of extremely hot and very highly pressurized gases in the normally hermetically sealed interior of the arrester housing. Thus, the interior surface of the arrester housing is subjected to an extremely high temperature and pressure while the exterior of the housing is substantially at ambient temperature and pressure. The resultant stresses on the arrester housing, typically formed of a ceramic material, such as porcelain, often cause the arrester housing to fracture and explode.

The fracture and explosion of the arrester housing is potentially dangerous to a person or property in the vicinity of the arrester. Thus, it is highly desirable that an arrester be provided with means for preventing the occurrence of such stresses to thereby prevent the explosion or fracture of the arrester housing. Further, in many cases, although the disconnector operates and removes an electrical lead from an arrester prior to the fracture and explosion of the arrester housing, sufficient internal very hot and very highly pressurized gases may have been generated to cause the arrester housing to explode when handled by a workman.

Several prior art disconnectors have been designed with this problem in mind. For example, the disconnector disclosed in the above mentioned U.S. Pat. No. 3,702,419 provides means for venting the gases, internally formed in an arrester housing, to the atmosphere upon the explosive operation of the disconnector. Another known prior art arrester provides for the leakage of gases internally formed in an arrester housing to the atmosphere through a leaky seal after the explosive operation of a disconnector. That is, the high pressure gases formed in the interior of the arrester housing cause the leakage of the gases to the atmosphere through the seal after the explosive operation of the disconnector.

In many cases, the above devices may not enable the venting of the gases internally formed in the arrester housings sufficiently rapidly to prevent the fracture and explosure of the housings. Further, the prior art leaky seal arrester is still considered to be a possible source of danger to a workman handling the arrester due to the possible presence of internally stored gases under pressure. A workman may also be hesitant to handle the arresters using these devices since there is no readily apparent visual indication that the internally formed gases have been vented to the atmosphere.

Finally, many prior art explosive electrical disconnectors include housings provided with reduced thickness portions to increase the speed or rate of fracture as a result of the tensile forces applied to the housings by the explosure operation of the disconnectors. An unfortunate disadvantage of such housings is their common reduced ability or capacity to withstand the application of inadvertent compressive forces resulting, for example, from the dropping of the disconnectors.

SUMMARY OF THE INVENTION An object of the present invention is to provide a new and improved arrester for protecting electrical equipment from damage or destruction due to electrical overvoltage surges.

Another object of the present invention is to provide a new and improved device for preventing the fracture and explosion of an arrester housing after the occurrence of an arrester failure.

'Another object of the present invention is to provide a new and improved electrical disconnector for removing an electrical lead from an arrester after the occurrence of an arrester failure.

Another object of the present invention is to providethe disconnector to enable the subsequent venting of the interior to the atmosphere after the explosive operation of the disconnector.

Another object of the present invention is to provide .a new and improved electrical disconnector including a housing with a reduced thickness portion and further including means for increasing the capacity of the disconnector housing to withstand the application of inadvertent compressive forces without fracturing.

- Another object of the present invention is to provide a new and improved explosive electrical disconnector for a surge arrester wherein the disconnector includes a housing having a reduced thickness portion and further includes means for increasing the capacity of the disconnector housing to withstand the application of inadvertent compressive forces without fracturing while substantially unaffecting the capacity of the disconnector housing to rapidly fracture upon the application of tensile forces resulting from the explosive operation of the disconnector.

Briefly, the device of the present invention comprises an explosive electrical disconnector for separating an electrical lead or terminal from a surge arrester and for interrupting the continuous flow of follow current through the arrester. The disconnector includes means for directly or positively venting the interior of the housing of the arrester to the disconnector prior to the explosive operation of the disconnector to enable the rapid venting of the interior to the atmosphere subsequent to the explosive operation of the disconnector.

The disconnector includes an insulating housing having a conductive explosive cartridge centrally disposed therein and spaced from the electric terminal to form a first air gap. The disconnector housing further includes a substantially flat upper surface and a plurality of upstanding bosses disposed thereon for supporting a resilient conductive member or'plate electrically connected to the cartridge. The conductive plate is electricallyconnected to and provides physical support for one or more of the internal components of the arrester. The volumetric space between the fiat upper surface of the disconnector housing and the lower surface of the conductive plate and between the upstanding bosses enables the direct or positive venting of the interior of I the arrester housing to the disconnector prior to the explosive operation of the disconnector to enable the rapid venting of the interior to the atmosphere subsequent to the explosive operation of the disconnector.

The device of the present invention further includes means for forming a second air gap between at least a portion of the cartridge and the electrical terminal substantially larger than the first gap upon the explosive operation of the disconnector to thereby aid in extinguishing an electrical are formed or maintained across the second gap to thereby interrupt the continuous flow of follow current. The explosive cartridge is initially positioned below the conductive'plate and, upon its ignition or explosion, deflects'at least a portion of the conductive plate away from the flat upper surface of the disconnector housing to thereby form the relatively large second gap.

Simultaneously, the disconnector housing is fractured by the explosion of the cartridge to propel the electrical lead or terminal away from the arrester, thereby further increasing the second gap. In this manner, an electrical arc across the second gap is rapidly extinguished to prevent the continued flow of the follow current.

Rapidly extinguishing the continuous flow of follow current terminates the formation of high pressure and high temperature gases within the interior of the arrester housing and thereby prevents an increase in stresses across the arrester housing. Simultaneously, the high pressure and high temperature. gases formed within the arrester housing during the continuous flow of follow current are vented tothe atmosphere to reduce the stresses across the arrester housing and to prevent the explosion or fracture of the arrester housing.

In a modified embodiment of the device of the present invention, the disconnector housing includes a reduced thickness portion to reduce its tensile strength and to thereby increase its fracture rate subsequent to the explosion of the cartridge. At least a portion of the upstanding circular bosses for supporting the conductive plate are disposed over the reduced thickness portion to increase the compressive strength of the disconnector housing and to thereby increasev its capacity or ability to withstand the application of inadvertent compressive forces.

BRIEF DESCRIPTION OF THE DRAWING The above and other objects and advantages and novel features of the present invention will become apparent from the following detailed description of an embodiment of the invention illustrated in the accompanying drawing wherein:

FIG. 1 is a front perspective view of a preferred embodiment of a surge arrester including an electrical disconnector constructed in accordance with the principles of the present invention;

FIG. 2 is a partially-elevational and partially-crosssectional view of the device of FIG. 1 taken along line 2-2 of FIG. 1;

FIG. 3 is cross-sectional view of the device of FIG. 1 taken along line 3-3 of FIG. 2;

FIG. 4 is an enlarged, fragmentary, cross-sectional view of a portion of the device of FIG. 1 taken along line 4-4 of FIG. 3;

FIG. 5 is an enlarged, fragmentary, detailed view of a portion of the device of the present invention illustrated in FIG. 4;

FIG. 6 is an enlarged, exploded, perspective view of a novel electrical disconnector constructed in accordance with the principles of the present invention;

FIG. 7 is an enlarged, fragmentary view, similar to the view of FIG. 4, of the device of the present invention during a portion of its operation; and

FIG. 8 is an enlarged, fragmentary view, similar to the view of FIG. 4, of an alternate embodiment of the device of the present invention.

Referring to the drawing an initially to FIGS. 1 and 2, there is illustrated a new and improved surge or lightning arrester 20 including a new and improved electrical disconnector 22 constructed in accordance with the principles of the present invention. The arrester 20 is provided to prtect comparatively expensive electrical equipment from damage or destruction due to electrical overvoltage surges, such as those caused by lightning strokes, by providing an electrical path through a ground lead to ground potential for the overvoltage surges. The new and improved disconnector 22 rapidly extinguishes an electrical arc to the ground lead from the arrester 20 or the disconnector 22 upon the explosive operation of the disconnector 22. The disconnector 22 further provides means for directly or positively venting the high pressure and high temperature gases formed in the interior of the arrester 20 due to the continuous flow of follow current therethrough. The disconnector 22 provides means for directly venting the interior of the arrester 20 to the disconnector 22 prior to the explosive operation of the disconnector 22 and to the atmosphere subsequent to the explosive operation of the disconnector 22.

The arrester 20 includes an elongated insulating housing 23 formed of any suitable insulating material, for example, a ceramic such as porcelain. The arrester 20 further includes an electrode assembly 24 formed by a plurality of electrodes 26 for providing a spark or air gap structure and a plurality of valve blocks 28, each formed of negative resistance material, disposed in the housing 23. The electrode assembly 24 and the valve blocks 28 are supported above the disconnector 22 by a spacer 30. The spacer 30 may take any convenient form, such as a V-shaped or a tubular cyclindricallyshaped spacer. A relatively thin, conductive support member or plate 32 is provided between the spacer 30 and the lowermost valve block 28 for supporting the valve blocks 28 above the spacer 30. A similar conductive support member or plate 34 is provided to separate and support the electrode assembly 24 above the valve blocks 28. The spacer 30 is in turn directly supported in the housing 23 by the disconnector 22.

The arrester 20 includes a first power lead terminal 36 for receiving a power lead to thereby apply line voltage to a first longitudinal end 38 of the arrester 20. The disconnector 22 supports a second ground lead terminal 48 for receiving a ground lead to thereby apply ground potential to the disconnector 22 positioned at a second longitudinal end 40 of the arrester 20.

The disconnector 22 is connected to the end 40 by a suitable rigid end member or bracket 42, normally formed of a conductive metal. The end 40 of the arrester 20 is hermetically sealed from the atmosphere by an elastomeric gasket 44 positioned between the end 40 and the disconnector 22. The disconnector 22 is biased against the gasket 44 to provide the required hermetic sealing force by a resilient member 46, which, in a preferred embodiment, is a Belleville washer. The resilient member 46 is in turn supported by the bracket 42.

The end 38 of the arrester 20 is also hermetically sealed from the atmosphere by an elastomeric gasket 50 positioned between the end 38 and a conductive support member 52 electrically connected to the terminal 36. The required hermetic sealing force is provided by a resilient member 54, similar to the member 46. The member 54 is, in turn, supported against the support member 52 by a suitable rigid end member or bracket 56, also normally formed of a conductive metal. Finally, a conductive resilient member or spring 58 is also provided to electrically connect the electrode assembly 24 to the power lead terminal 36.

Referring more specifically to FIGS. 3 through 6, the 8 device of applicants invention comprises a disconnector 22 for explosively separating the terminal 48 and a ground lead attached thereto from the arrester 20 after the failure of the arrester to interrupt the continuous flow of follow current. In accordance with an important feature of the present invention, the disconnector 22 provides means for directly or positively venting the interior of the housing 23 to the disconnector 22 prior to the explosive operation of the disconnector 22 and to the atmosphere subsequent to the explosive operation of the disconnector 22. Although the interior of the housing 23 is not sealed from the disconnector 22 prior to the explosive operation of the disconnector 22, the interior of the housing 23 is in fact hermetically sealed from the atmosphere by the gaskets 44 and 50, referred to above.

In accordance with an important feature of the present invention, the disconnector 22 includes a relatively thin, conductive support member or plate 60 that physically supports the spacer 30 Within the housing 23. The conductive plate 60 is formed of a conductive metal that is sufficiently resilient to permit at least a portion of the plate 60 to be bent or deflected towards the interior of the housing 23. The outer periphery of the plate 60 is also substantially less than the facing inner periphery of the housing 23 to prevent the sealing of the interior of the housing 23 by the plate 60.

The disconnector 22 further includes a frangible insulating housing 62 for physically supporting the components of the disconnector 22. Preferably, the housing 62 is formed of a phenolic material. The housing 62 includes a relatively flat upper surface 64 for compressively engaging the gasket 44. The surface 64 further includes a plurality of integrally formed, upstanding members or bosses 66 and 68 for supporting the plate 60. The bosses 68 include upstanding locating members 70 for receipt within a plurality of locating apertures 72 in the plate 60 for correctly positioning the plate 60 above the housing 62. The bosses 66 include apertures 74 for receiving one or more rivets 76 through one or more apertures 77 in the plate 60. In a specific embodiment, it has been found that a single rivet 76 is sufficient to securely maintain the plate 60 in position above the housing 62 on the bosses 66 and 68.

In accordance with an important feature of the present invention, the means for directly or positively venting the interior of the housing 23 to the disconnector 22 is the volumetric space between the lower portion of the plate 60 and the upper surface 64 of the housing 62 and the separation or space between the bosses 66 and 68.

The housing 62 includes centrally disposed, generally circular aperture 78 for housing'various components of the disconnector 22. For example, an upper conductive mounting or locking portion 80 of the terminal 48 is positioned in the lowermost portion of the aperture 78. An annular resistive element 82 is provided immedi- 7 ately above and in electrical contact with the conductive portion 80, for shunting capacitive leakage currents, generated by the-presence of normal line voltage across the arrester 20 to the terminal 48. Centrally dis-' posed within both the aperture 78 and the resistive element 82 is an explosive cartridge or rivet 84.-

The cartridge 84 includes a centrally disposed charge of explosive material 86 sealed within the cartridge 84 by any suitable sealing means 88. The lowermost end of the cartridge 84 is terminated by a conductive member or cap 90 formed, in a preferred embodiment, of brass. The cap 90'is positioned within a centrally disposed aperture 92 forr'ned in the upper portion 80 of the terminal '48 and ismaintained in a substantially fixed, centrally disposed position within the aperture 92 by the annular resistive element 82. The inner periphery of the aperture 92 is preferably greater by a predetermined amount than the facing outer periphery of the cap 90 to thereby form an annular spark or air gap 94 of predetermined dimensions.

An upper portion or head portion 96 of the cartridge 84 is maintained in electrical contact with the plate 60 by a resilient conductive member or washer 98. Thus, capacitive leakage currents resulting from the presence of normal line voltage across the arrester 20 are transferred from the plate 60 to the head portion 96 of the cartridge 84 through the washer 98 and the resistive element 82 to the terminal 48. The resistive element 82 thereby prevents the formation of an electrical arc in the gap 94 during the presence of normal line voltage across the arrester 20. Since an electrical arc, is not formed across the gap 94 during the presence of normal line voltage across the arrester 20, the explosive cartridge 84 is prevented from being sufficiently heated to cause the ignition of the explosive charge 86.

Upon the occurrence of an overvoltage surge, for example, as would occur as a result of a lightning stroke, thev gap structure of the electrodeassembly 24 breaks down electrically to permit the flow of surge current through the lightning arrester 20. The magnitude of the surge current resulting from the overvoltage surge is sufficient to electrically break down the gap 94 and to thereby cause an electrical arc to be formed across the gap 94. The presence of the electrical arc across the gap 94 causes the heating of the explosive cartridge 84.

If the lightning arrester 20 is operating in a normal manner, after the termination of the relatively brief overvoltage surge, the arrester 20 may conduct follow current. The gap structure of the electrode assembly 24 normally interrupts the flow of follow current after one or a small number of half cycles of the follow current. Follow current is the current that may flow through the arrester due to the normal line voltage across the arrester and subsequent to the flow of surge current through the arrester.

The flow of follow current through the arrester 20 maintains an electrical arc across the gap 94 to thereby continue the heating of the explosive cartridge 84. As soon as the gap structure of the electrode assembly 24 interrupts the flow of follow current, the electrical arc in the gap 94 is extinguished or terminated to thereby prevent the further heating of the explosive cartridge 84. ln this manner, the arrester 20 is returned to a condition for shunting subsequent overvoltage surges to ground and to thereby protect its associated electrical equipment.

If, as occasionally occurs, the gapstructure of the reason fails to interrupt the flow of follow current, a fault condition is present which necessitates the" removal of the arrester 20 from the electricalcircuit. An overvoltaage surge and its associated surge current occasionally are sufficiently large to permanently damage or deteriorate the gap structure of the electrode assembly 24 of the arrester 20 to prevent the arrester 20 from subsequently properly functioning. One common manner in which the gap'structure of the arrester 20 is damaged by the flow of surge current of a large magnitude is by the generation and flow of molten metal from'the electrodes 26 of the electrode assembly 24 in response to the heat generated by the surge current. This molten metal may subsequently distort one or more of the gaps between the electrodes 26 of the assembly 24 or may in fact weld two or more of the electrodes 26 together to thereby reduce the ability of the gap structure of the electrode assembly 24 to interrupt the flow of follow current. Thus, follow current is not terminated and continues to flow through the arrester 20 causing the valve blocks 28 to continuously heat, thereby reducing the electrical resistance of the valve blocks 28. Thus,

the follow current increases with each successive half cycle. In this condition, the arrester housing 23 may fracture and explode. Furthermore, circuit fuses may be blown or circuit breakers may operate in response to the ever increasing follow current flowing through the arrester 20.

These deleterious effects may be prevented in the following manner. The continuous flow of follow current maintains an electrical arc across the gap 94 to continuously heat the explosive cartridge 84. When the cartridge 84 is sufficiently heated to raise the charge 86 to its ignition temperature, the charge 86 explodes (FIG. 7) to provide a force to fracture the housing 62 and to thereby separate the terminal 48 and the ground lead attached thereto from the arrester 20. In accordance with an important feature of the present invention, the disconnector 22 provides means for rapidly increasing the gap across which an electrical arc must be maintained to permit the continued flow of follow current. As illustrated in FIG. 7, upon the ignition or explosion of the explosive charge 86, the cartridge 84 is normally separated into at least a lower portion 100 and an upper portion 102. The lower portion 100 is effectively expanded into the resistive element 82 and the upper portion of the ground lead terminal 48 in response to the radially outward force provided by the ignited explosive charge 86. The upper portion 102 is severed from the lower portion and propelled against the plate 60 to bend, deflect or bulge the plate 60 and to thereby instantaneously form a relatively large gap 104 which, together with the exploding gases of the ignited cartridge 84, is effective to interrupt the continuous flow of follow current. The upward force provided by the ignited explosive charge 86 causes the upper portion 102 to bend, bow or deflect at least the central portion of the plate 60 to rapidly form the relatively large gap 104.

A downward force provided by the ignited explosive charge 86 subjects the housing 62 to a relatively large tensile force. Since a characteristic of phenolics and similar materials commonly used to form the housing 62 is their relative weakness in tension, the housing 62 fractures normally along the fracture lines 106 to enable the terminal 48 and the ground lead attached thereto to be propelled from the arrester 20. The dotted line portion of FIG. 7 illustrates the terminal 48 being propelled from the arrester after the fracture of the housing 62. As the distance between the moving terminal 48 and the arrester 20 increases, the gap 104 also correspondingly increases. Thus, the continuous flow of follow current is rapidly interrupted.

As is apparent, the propulsion of the terminal 48 from the arrester 20 further enables the gases generated in the interior of the arrester 20 by the flow of follow current to be rapidly vented to the atmosphere through the vent space described above and the aperture formed in the housing 62 due to the severing of the terminal 48 from the housing 62. Thus, in accordance with the principles of the present invention, the housing 23 of the arrester 20 is prevented from being sufficiently stressed to cause the fracture and explosion of the housing 23.

Thus, the possibility of the fracture and explosion of the housing 23 is reduced by several features of the present invention. First, the rapid formation of a relatively large gap 104 upon the explosion of the cartridge 84 enables the relatively rapid interruption of the continuous flow of follow current to thereby prevent the further formation and build up of high pressure, high temperature gases in the interior of the housing 23. Secondly, the provision of the direct or positive venting of the interior of the housing 23 to the disconnector 22 prior to the explosive operation of the disconnector 22 and to the atmosphere upon the explosive operation of the disconnector 22 by the means described above enables the high pressure and high temperature gases formed within the housing 23during the flow of follow current to be rapidly vented to the atmosphere and to thereby reduce the stresses across the housing 23.

In accordance with an important feature of the present invention, the outer periphery of the housing 62, in one embodiment, is maintained slightly less than the periphery of the facing inner surface of the bracket 42 to thereby enable a major portion of the housing 62 to move in a radial direction away from the upper portion 80 of the terminal 48 toward the facing inner surface of the bracket 42 in response to the radially outward force provided by the ignited explosive charge 86. This radial movement of the major portion of the housing 62 facilitates and increases the speed or rate of fracture along the fracture lines 106. Thus, the terminal 48 and the ground lead attached thereto are more rapidly separated from the housing 62, the disconnector 22 and the arrester 20.

In an alternate embodiment of the present invention, the housing 62 (FIG. 8) of the disconnector 22 is formed with a reduced thickness, notched or cut-away portion 108 to thereby aid in the fracturing of the housing 62 generally along the fracture lines 110 in response to the application of the tensile forces to the housing 62 from the explosion of the cartridge 84.-

In accordance with an important feature of the present invention, at least a portion of each of the bosses 66 and 68 are located over the reduced thickness portion 108 to thereby bridge the reduced diameter portion 108 and strengthen the housing 62, increasing its ability or capacity to withstand the application of inadvertent compressive forces. Inadvertent compressive forces may be applied to the housing 62 by, for example, the dropping of the arrester 20 on the terminal 48 or by the application of an excessive compressive force on the terminal 48 by a workman handling the arrester 20.

The provision of the bosses 66 and 68 as bridging portions over the reduced diameter portion 108 increases the compressive strength of the housing 62 in the area or region of the reduced thickness portion 108. At the same time, however, the addition of the bosses 66 and 68 over the reduced thickness portion 108 does not significantly affect the ability or capacity of the housing 62 to fracture along the fracture lines 110 in response to the application of the tensile forces resulting from the explosion of the cartridge 84.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. Thus, it is to be understood, that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described above.

What is claimed and desired to be secured by Letters Patent of the United States is:

l. A disconnector for a surge arrester of the type having a first elongated insulating arrester housing and arrester components disposed in the interior of said first housing, said disconnector comprising an electrical terminal,

means for supporting said terminal,

means for separating said terminal from said supporting means upon the occurrence of a fault condition and means for directly or positively venting the interior of said first housing to the interior of said disconnector prior to the operation of said separating means and to the atmosphere subsequent to the operation of said separating means.

2. A disconnector as defined in claim 1 wherein said terminal comprises a ground lead terminal. v

3. A disconnector as defined in claim I wherein said supporting means comprises a second insulating housing.

4. A disconnector as defined in claim 3 further comprising means for securely maintaining said disconnector in engagement with one longitudinal end portion of said first housing.

5. A disconnector as defined in claim 3 wherein said second housing includes a substantially planar surface and a centrally disposed aperture.

6. A disconnector as defined in claim 5 further comprising a conductive member spaced from said centrally disposed aperture for supporting at least one of said arrester components.

7. A disconnector as defined in claim 6 wherein said separating means comprises a conductive explosive cartridge disposed in said aperture.

8. A disconnector as defined in claim 7 further comprising means for maintaining said cartridge in electrical contact with said conductive member.

9. A disconnector as defined in claim 8 further comprising means for positioning said cartridge in said aperture to form a first spark gap between said cartridge and said terminal of sufficient dimensions to prevent the generation of an electrical arc thereacross when a voltage in a normal operating range is present across said arrester and to enable the generation of an electrical arc across said first gap when a voltage greater than 10. A disconnector as defined in claim 9 wherein said i cartridge is positioned to form a second spark gap by deflecting at least a portion-of said conductive member generally away from said planar surface upon the explosive operation of said cartridge, said second gap being more resistant to the generation vormaintenance of an electricarcthereacross than said first gap... I

v l A.disc onnector as'defined. in claim9 wherein said positioning .means comprises an annular resistance v means, said resistance means providing an electric path for transmitting capacitive ,leakage currents passing through said. arrester to said terminal. I

12. A disconnector as defined in claim 6 wherein said planar surface. includes one or moreprotrudingmembers disposed thereon forphysically supporting said conductive member.

13'. A disconnector as defined in claim 12 wherein said protruding members comprise bosses integrally formed with said second housing.

Adisconnector as defined in claim 12- wherein said venting means comprises the volumetric space or spaces bounded by said conductive member, said substantially planarsurface and said one or more protruding members. I

15. A disconnector as defined in claim 1 wherein said separatingmeans comprises aconductive explosive cartridge.

.16. A disconnectoras defined in claim l further comprising means for positioning. sai'd cartridge with respect to said terminal to form a first spark gap between said terminal and said conductive cartridge of sufficient dimensions to prevent the generation of an electrical arc thereacross when a voltage in a normal operating range is present across said arrester and to enable the generation of an electrical arc across. said first gap when a voltage greater than the voltages within said normal, operating range isv present across said arrester..

1.7.A disconnector as defined in, claim 16 further comprising means for forming a second spark gap upon the explosive operation of said cartridge, said second arrester components disposed in the interior of said first housing, said disconnector comprising an electrical terminal, means for supporting said terminal, said supporting means comprising a second insulating housing, means for separating said terminal from said supporting means upon the occurrence of a fault condition,

means for directly or positively venting the interior of I said first housing to said disconnector prior to the operation of said separating means and to the atmosphere subsequent to the operation of said separating means and 12 means for securely maintaining said disconnector in engagement with one longitudinal end portion of said first housing,said 'securely maintaining means comprising a relatively rigid bracket having an inner periphery surrounding and substantially greater than the periphery of the facing outer surfaceof said second housingto the'reby.enablej at least a portionof said facing surface tomove in the direction of said inner'periphery upon the operation of said separating means, 4 20. A disconnector fora surge arrester comprising an electrical terminal, i j I means for supporting said terminal, said supporting means comprising an insulating housing and means for securely. maintaining said disconnector in a sealed engagement with one longitudinal end portion of said arrester, said maintaining means having an inner periphery surrounding and of a greater magnitude than the periphery of the outer facing surface of said housing to thereby form a substantial gap the'rebetween. 21. A disconnector for a surge arrester comprising an electrical terminal, 5 means for'supporting said terminal, said supporting means comprising an-insulating housing, I means for securely maintaining said disconnector in a sealed engagement with one longitudinal end portion of said arrester, said maintaining means having an innerperiphery surrounding andof a greater magnitude than the peripheryofthe outer facing surface of saidhousing to thereby-forma substantial-gap therebetween, and i means for separating said terminal'from said housing uponthe occurrenc'e'of a fault'condition, atleast a portion of said facing surface of said housing being moved across said gap towards said inner. pe-

riphery of said maintaining means by said separatingmeans upon the means.

22. A disconnector comprising an electrical terminal, 1 i

operation of said separating means for supporting said terminaL'said supporting means comprising an insulatinghousing, said'housing including a planar surface and a reduced thickness portion for reducing the capacity of said housing to 'withstandthe application of tensile forces without fracturing, said reduced thickness portion comprising a notched or cut-away portion of said 'housing, and

means for increasing the capacity of said housing to withstand the application of compressive forces without fracturing across said notchedor cut-away I a the application of tensile forces.

24. A disconnector as defined in claim 23 wherein said housing is formed of a phenolic material.

25. A disconnector for a surge arrester'comprising an electrical.-terminal,

means for automatically separating said terminal from said disconnector upon the occurrence of a fault condition,

means for forming a first spark gap defining the path of an electrical arc prior to the operation of said separating means and means for forming a second spark gap upon the operation. of said separating means and independently of the separation of said terminal from said disconnector, said second gap being more resistant to the maintenance of said electrical arc thereacross than said first gap.

26. A disconnector as defined in claim wherein said separating means comprises a conductive explosive cartridge and wherein said second gap forming means comprises an .electrically conductive member conductively disposed with respect to said cartridge and having at least a portion thereof deflected by said cartridge to form at least a portion of said second gap upon the explosive operation of said cartridge.

27. A disconnector asdefined in claim 26 further comprising an insulating housing for supporting said terminal, said housing having a planar surface and a centrally disposed, elongated aperture, said terminal being fixedly positioned in a first longitudinal portion of said aperture and at least a portion of said cartridge being positioned in a second longitudinal portion of said aperture and spaced from said terminal to form said first gap.

28. A disconnector as defined in claim 27 wherein said housing includes a plurality of integrally formed,

first housing and said interior portion of said second housing from the atmosphere and means for directly or positively venting the interior of said first housing to said interior portion of said second housing prior to the operation of said separating means and to the atmosphere subsequent to the operation of said separating means.

30. A surge arrester as defined in claim 29 wherein said second housing includes a substantially planar surface and a centrally disposed aperture.

31. A surge arrester as defined in claim 30 wherein said separating means further includes a conductive member spaced from said centrally disposed aperture.

32. A surge arrester as defined in claim 31 wherein said separating means comprises a conductive explosive cartridge disposed in said aperture.

33. A surge arrester as defined in claim 32 further 14 comprising means for maintaining said cartridge in electrical contact through a low resistance path with said conductive member.

34. A surge arrester as defined'in claim 33 further comprising means for positioning said cartridge in said aperture to form a first spark gap between said cartridge and said secondterminal of sufficient dimensions to prevent the generation of an electrical arc thereacross when a voltage in a normal operating range is present across said arrester and to enable the generation of an electrical arc across said first gap when a voltage greater than the voltages within that normal operating range is present across said arrester.

35. A surge arrester as defined in claim 34 wherein said cartridge is positioned to form a second spark gap upon the explosive operation of said cartridge, said second gap being more resistant to the generation or maintenance of an electrical arc thereacross than said first gap.

36. A surge arrester as defined in claim 34 wherein said positioning means comprises an annular resistance means, said resistance means providing an electrical path for transmitting capacitive leakage currents passsing through said arrester to said second terminal.

37. A surge arrester as defined in claim 31 wherein said planar surface includes one or more protruding members disposed thereon for physically supporting said conductive member.

38. A surge arrester as defined in claim 37 wherein said protruding members comprise bosses integrally formed with said second housing.

39. A surge arrester as defined in claim 37 wherein said venting means comprises the volumetric space or spaces bounded by said conductive member, said substantially planar surface and said one or more protruding members.

40. A surge arrester as defined in claim 29 wherein said separating means includes a conductive explosive cartridge.

41. A surge arrester as defined in claim 40 further comprising means for positioning said cartridge with respect to said second terminal to form a first spark gap of sufficient dimensions to prevent the generation of an electrical arc thereacross when a voltage in a normal operating range is present across said arrester and to enable the generation of an electrical arc across said first gap when a voltage greater than the voltages within said normal operating range is present across said arrester.

42. A surge arrester as defined in claim 41 further comprisingmeans for forming a second spark gap upon the explosive operation of said cartridge, said second gap being more resistant to the generation or maintenance of an electrical arc thereacross than said first gap upon the explosive operation of said cartridge. =1 l 

1. A disconnector for a surge arrester of the type having a first elongated insulating arrester housing and arrester components disposed in the interior of said first housing, said disconnector comprising an electrical terminal, means for supporting said terminal, means for separating said terminal from said supporting means upon the occurrence of a fault condition and means for directly or positively venting the interior of said first housing to the interior of said disconnector prior to the operation of said separating means and to the atmosphere subsequent to the operation of said separating means.
 2. A disconnector as defined in claim 1 wherein said terminal comprises a ground lead terminal.
 3. A disconnector as defined in claim 1 wherein said supporting means comprises a second insulating housing.
 4. A disconnector as defined in claim 3 further comprising means for securely maintaining said disconnector in engagement with one longitudinal end portion of said first housing.
 5. A disconnector as defined in claim 3 wherein said second housing includes a substantially planar surface and a centrally disposed aperture.
 6. A disconnector as defined in claim 5 further comprising a conductive member spaced from said centrally disposed aperture for supporting at least one of said arrester components.
 7. A disconnector as defined in claim 6 wherein said separating means comprises a conductive explosive cartridge disposed in said aperture.
 8. A disconnector as defined in claim 7 further comprising means for maintaining said cartridge in electrical contact with said conductive member.
 9. A disconnector as defined in claim 8 further comprising means for positioning said cartridge in said aperture to form a first spark gap between said cartridge and said terminal of sufficient dimensions to prevent the generation of an electrical arc thereacross when a voltage in a normal operating range is present across said arrester and to enable the generation of an electrical arC across said first gap when a voltage greater than the voltages within said normal operating range is present across said arrester.
 10. A disconnector as defined in claim 9 wherein said cartridge is positioned to form a second spark gap by deflecting at least a portion of said conductive member generally away from said planar surface upon the explosive operation of said cartridge, said second gap being more resistant to the generation or maintenance of an electric arc thereacross than said first gap.
 11. A disconnector as defined in claim 9 wherein said positioning means comprises an annular resistance means, said resistance means providing an electric path for transmitting capacitive leakage currents passing through said arrester to said terminal.
 12. A disconnector as defined in claim 6 wherein said planar surface includes one or more protruding members disposed thereon for physically supporting said conductive member.
 13. A disconnector as defined in claim 12 wherein said protruding members comprise bosses integrally formed with said second housing.
 14. A disconnector as defined in claim 12 wherein said venting means comprises the volumetric space or spaces bounded by said conductive member, said substantially planar surface and said one or more protruding members.
 15. A disconnector as defined in claim 1 wherein said separating means comprises a conductive explosive cartridge.
 16. A disconnector as defined in claim 15 further comprising means for positioning said cartridge with respect to said terminal to form a first spark gap between said terminal and said conductive cartridge of sufficient dimensions to prevent the generation of an electrical arc thereacross when a voltage in a normal operating range is present across said arrester and to enable the generation of an electrical arc across said first gap when a voltage greater than the voltages within said normal operating range is present across said arrester.
 17. A disconnector as defined in claim 16 further comprising means for forming a second spark gap upon the explosive operation of said cartridge, said second gap being more resistant to the generation or maintenance of an electric arc thereacross than said first gap.
 18. A disconnector as defined in claim 17 wherein said second gap forming means comprises a conductive member conductively disposed with respect to said cartridge and having at least a portion thereof deflected by said cartridge to form at least a portion of said second gap upon the explosive operation of said cartridge.
 19. A disconnector for a surge arrester of the type having a first elongated insulating arrester housing and arrester components disposed in the interior of said first housing, said disconnector comprising an electrical terminal, means for supporting said terminal, said supporting means comprising a second insulating housing, means for separating said terminal from said supporting means upon the occurrence of a fault condition, means for directly or positively venting the interior of said first housing to said disconnector prior to the operation of said separating means and to the atmosphere subsequent to the operation of said separating means and means for securely maintaining said disconnector in engagement with one longitudinal end portion of said first housing, said securely maintaining means comprising a relatively rigid bracket having an inner periphery surrounding and substantially greater than the periphery of the facing outer surface of said second housing to thereby enable at least a portion of said facing surface to move in the direction of said inner periphery upon the operation of said separating means.
 20. A disconnector for a surge arrester comprising an electrical terminal, means for supporting said terminal, said supporting means comprising an insulating housing and means for securely maintaining said disconnector in a sealed engagement with one longitudinal end portion of said arrester, said maintaining means having an inner periphery surrounding and of a greater magnitude than the periphery of the outer facing surface of said housing to thereby form a substantial gap therebetween.
 21. A disconnector for a surge arrester comprising an electrical terminal, means for supporting said terminal, said supporting means comprising an insulating housing, means for securely maintaining said disconnector in a sealed engagement with one longitudinal end portion of said arrester, said maintaining means having an inner periphery surrounding and of a greater magnitude than the periphery of the outer facing surface of said housing to thereby form a substantial gap therebetween, and means for separating said terminal from said housing upon the occurrence of a fault condition, at least a portion of said facing surface of said housing being moved across said gap towards said inner periphery of said maintaining means by said separating means upon the operation of said separating means.
 22. A disconnector comprising an electrical terminal, means for supporting said terminal, said supporting means comprising an insulating housing, said housing including a planar surface and a reduced thickness portion for reducing the capacity of said housing to withstand the application of tensile forces without fracturing, said reduced thickness portion comprising a notched or cut-away portion of said housing, and means for increasing the capacity of said housing to withstand the application of compressive forces without fracturing across said notched or cut-away portion of said housing, said increasing means comprising at least one integrally formed mass protruding from said planar surface and at least partially overlying said notched or cut-away portion.
 23. A disconnector as defined in claim 22 wherein said increasing means comprises a plurality of masses protruding from and disposed about said planar surface and integrally formed with said housing, said masses being so disposed on said planar surface to substantially unaffect the capacity of said housing to fracture upon the application of tensile forces.
 24. A disconnector as defined in claim 23 wherein said housing is formed of a phenolic material.
 25. A disconnector for a surge arrester comprising an electrical terminal, means for automatically separating said terminal from said disconnector upon the occurrence of a fault condition, means for forming a first spark gap defining the path of an electrical arc prior to the operation of said separating means and means for forming a second spark gap upon the operation of said separating means and independently of the separation of said terminal from said disconnector, said second gap being more resistant to the maintenance of said electrical arc thereacross than said first gap.
 26. A disconnector as defined in claim 25 wherein said separating means comprises a conductive explosive cartridge and wherein said second gap forming means comprises an electrically conductive member conductively disposed with respect to said cartridge and having at least a portion thereof deflected by said cartridge to form at least a portion of said second gap upon the explosive operation of said cartridge.
 27. A disconnector as defined in claim 26 further comprising an insulating housing for supporting said terminal, said housing having a planar surface and a centrally disposed, elongated aperture, said terminal being fixedly positioned in a first longitudinal portion of said aperture and at least a portion of said cartridge being positioned in a second longitudinal portion of said aperture and spaced from said terminal to form said first gap.
 28. A disconnector as defined in claim 27 wherein said housing includes a plurality of integrally formed, protruding members disposed on said planar surface for positioning said conductive member.
 29. A surge arrester comprising a first elongated insulating housing having fiRst and second, oppositely disposed, longitudinal ends, a first electrical terminal disposed at said first end, a second electrical terminal disposed at said second end, means for separating said second terminal from said arrester upon the occurrence of a fault condition, said separating means comprising a second insulating housing, said second housing including an interior portion and an exterior portion, means for hermetically sealing the interior of said first housing and said interior portion of said second housing from the atmosphere and means for directly or positively venting the interior of said first housing to said interior portion of said second housing prior to the operation of said separating means and to the atmosphere subsequent to the operation of said separating means.
 30. A surge arrester as defined in claim 29 wherein said second housing includes a substantially planar surface and a centrally disposed aperture.
 31. A surge arrester as defined in claim 30 wherein said separating means further includes a conductive member spaced from said centrally disposed aperture.
 32. A surge arrester as defined in claim 31 wherein said separating means comprises a conductive explosive cartridge disposed in said aperture.
 33. A surge arrester as defined in claim 32 further comprising means for maintaining said cartridge in electrical contact through a low resistance path with said conductive member.
 34. A surge arrester as defined in claim 33 further comprising means for positioning said cartridge in said aperture to form a first spark gap between said cartridge and said second terminal of sufficient dimensions to prevent the generation of an electrical arc thereacross when a voltage in a normal operating range is present across said arrester and to enable the generation of an electrical arc across said first gap when a voltage greater than the voltages within that normal operating range is present across said arrester.
 35. A surge arrester as defined in claim 34 wherein said cartridge is positioned to form a second spark gap upon the explosive operation of said cartridge, said second gap being more resistant to the generation or maintenance of an electrical arc thereacross than said first gap.
 36. A surge arrester as defined in claim 34 wherein said positioning means comprises an annular resistance means, said resistance means providing an electrical path for transmitting capacitive leakage currents passsing through said arrester to said second terminal.
 37. A surge arrester as defined in claim 31 wherein said planar surface includes one or more protruding members disposed thereon for physically supporting said conductive member.
 38. A surge arrester as defined in claim 37 wherein said protruding members comprise bosses integrally formed with said second housing.
 39. A surge arrester as defined in claim 37 wherein said venting means comprises the volumetric space or spaces bounded by said conductive member, said substantially planar surface and said one or more protruding members.
 40. A surge arrester as defined in claim 29 wherein said separating means includes a conductive explosive cartridge.
 41. A surge arrester as defined in claim 40 further comprising means for positioning said cartridge with respect to said second terminal to form a first spark gap of sufficient dimensions to prevent the generation of an electrical arc thereacross when a voltage in a normal operating range is present across said arrester and to enable the generation of an electrical arc across said first gap when a voltage greater than the voltages within said normal operating range is present across said arrester.
 42. A surge arrester as defined in claim 41 further comprising means for forming a second spark gap upon the explosive operation of said cartridge, said second gap being more resistant to the generation or maintenance of an electrical arc thereacross than said first gap.
 43. A surge arrester as defined in claim 42 wherein said second gap forming means comprises a conductive member conductively disposed with respect to said cartridge and having at least a portion thereof deflected by said cartridge to form at least a portion of said second gap upon the explosive operation of said cartridge. 